Anionic cellulose ethers having temperature-dependent associative properties

ABSTRACT

An anionic cellulose ether obtainable by a process comprising reacting an alkali metal cellulose with one or more reagents A selected from the group consisting of haloacetic acids, alkali metal haloacetates, alkali metal vinyl sulfonates, vinyl sulfonic acid, and precursors thereof, and one or more reagents B having the formula R 1 —(OCH 2 CH(R 2 )) n -P, wherein R 2  represents hydrogen or a methyl group; n is 0-2; P represents a glycidyl ether group, a 1,2-epoxy group or a precursor thereof, if P represents a glycidyl ether group, R 1  represents a linear C 3 -C 5  alkyl group, optionally containing an oxygen atom, a phenyl group, or a benzyl group, and if P represents a 1,2-epoxy group, R 1  represents a linear C 3 -C 5  alkyl group, optionally containing an oxygen atom. Preferably, reagent A is chloroacetic acid and reagent B is n-butyl glycidyl ether. The invention also relates to the use of said anionic cellulose ether as an associative thickener, rheology modifier or stabilizer.

This application is the national phase of PCT/EP99/09662, filed Dec. 7,1999, which claims the benefit of U.S. Provisional Application No.60/112,300, filed Dec. 14, 1998 and of European Patent Application No.98204186.5, filed Dec. 11, 1998.

FIELD OF THE INVENTION

The invention relates to anionic cellulose ethers and to the use of saidethers as associative thickeners, rheology modifiers or stabilizers.

BACKGROUND OF THE INVENTION

Associative thickeners, rheology modifiers, and stabilizers foremulsions and suspensions are used in many applications includingwater-based paints, (oil) drilling, paper making, (laundry) detergents,and personal care products or cosmetics. However, most compoundstypically used in these applications suffer from the disadvantage thatthe viscosity of the composition decreases with increasing temperature.In other words, the performance of these compounds is poorer at highertemperatures, typically in the range of 20 to 60° C.

EP-A1-0 853 159 relates to a process and a coating colour for coating acellulosic web. It is described that the coating colour contains anaqueous polymer whose viscosity in an aqueous solution increases whenthe temperature rises. Preferably, methyl cellulose is used. In FIG. 3it is shown that carboxymethyl cellulose is not subject to an increasein viscosity with increasing temperature.

Although this document does not pertain to anionic cellulose ethers ofthe type disclosed below, it describes the effect which is also desiredin the present application. A drawback to the use of the celluloseethers disclosed in EP-A1-0 853 159 is that with increasing temperaturethe solubility of the polymer is lost completely. In fact, the transientincrease in viscosity is caused by the loss of solubility of the polymerwith increasing temperature. Hence, it is the aim of the presentapplication to provide alternatives to these polymers which do not havethis disadvantageous property.

Anionic cellulose ethers are known in the art. There are severaldocuments showing that hydrophobically modified cellulose ethers haveassociative properties and cause thickening of compositions containingthem.

EP-A1-0 566 911 pertains to hydrophobically modified polysaccharideethers, having a molecular weight of 10,000 to 300,000, which aresubstituted with hydrophobic alkyl or alkaryl groups having 8 to 24carbon atoms and which can be used as associative thickeners in aqueousprotective coatings. Table 4 discloses carboxymethyl hydroxypropylstarch substituted with C₁₈ hydrophobic groups and carboxymethylhydroxyethyl cellulose substituted with C₁₆ hydrophobic groups. Thesecompounds were prepared, according to the footnote of Table 4, byreacting carboxymethyl hydroxypropyl starch and carboxymethylhydroxyethyl cellulose with stearyl isocyanate using dimethyl sulfoxideas a solvent.

JP-A-09110901 relates to carboxymethyl polysaccharide ethers substitutedwith a C₈-C₄₀, optionally branched alkyl or alkenyl glycidyl ether andtheir use as a thickening agent for cosmetics and toiletries. InExamples 1-14, carboxymethyl hydroxyethyl cellulose, carboxymethylmethyl cellulose, and carboxymethyl hydroxypropyl starch substitutedwith stearyl, palmityl, behenyl or isostearyl glycidyl ether groups aredisclosed. These compounds are prepared by reacting the polysaccharide,e.g. hydroxyethyl cellulose, with the glycidyl ether, followed bycarboxymethylation.

Similar types of compounds, e.g. carboxymethyl hydroxypropyl methylcellulose substituted with stearyl glycidyl ether groups, andpreparative processes are described in JP-A-05331201. Said compounds arereported to be used as thickening agents in cataplasm and cosmeticcompositions.

WO 97/31950 pertains to carboxymethyl cellulose ethers substituted withlong-chain groups and their use as thickening additives for aqueouscompositions such as paints, plasters, and cosmetics. On page 7 of thisdocument said cellulose ethers are reported to possess high associativeproperties. In Example 1, carboxymethyl cellulose is reacted with1-epoxyoctadecane and in Example 19; carboxymethyl cellulose is reactedwith dodecyl glycidyl ether.

DE-A1-3927567 pertains to the use of hydrophobically modified celluloseethers for stabilizing aqueous coal slurries. These cellulose ethers aresubstituted with hydrophobic groups having at least six carbon atoms inthe form of, inter alia, 3-alkoxy-2-hydroxypropyl and2-alkyl-2-hydroxyalkyl groups. In column 4, lines 15-16, n-butylglycidyl hydroxyethyl cellulose is exemplified.

EP-A2-0 295 628 relates to water-soluble 3-alkoxy-2-hydroxypropylderivatives of hydroxyethyl, hydroxypropyl, and methyl cellulose ethersand their use in building compositions. The alkyl group is a straight-or branched-chain alkyl group having 2 to 8 carbon atoms. As is shown inExample 1, these compounds are prepared in a slurry process by reactionof hydroxyethyl cellulose with n-butyl glycidyl ether.

However, none of these prior art documents describes the desiredviscosity-temperature relationship explained above. It is furtherexpected that the cellulose ethers which are disclosed in thesedocuments will have decreasing viscosity with increasing temperature.

EP-A1-0 541 939 discloses a number of 3-allyloxy-2-hydroxypropyl ethersof celluloses substituted with other ether groups including methyl3-allyloxy-2-hydroxypropyl cellulose, hydroxyethyl3-allyloxy-2-hydroxypropyl cellulose, and carboxymethyl3-allyloxy-2-hydroxy-propyl cellulose. These water-soluble celluloseethers are polymerizable, which may be advantageous in someapplications. However, cellulose ethers containing allyl groups areunstable compounds and will decompose gradually upon storage. This,obviously, is a disadvantage and for this reason such compounds are notdesired for use in applications in accordance with the presentinvention.

Surprisingly, we have found anionic cellulose ethers which show a lesserdecrease, or even an increase, in viscosity with an increase intemperature, and this effect is believed to be due to a reversibletemperature-dependent association. Furthermore, unlike some of the(associative) thickeners of the prior art, the compounds of theinvention retain their good water solubility even at highertemperatures. These properties make them particularly suitable for usein the applications mentioned above, in particular in drillingoperations in which they are expected to reduce fluid loss.

SUMMARY OF THE INVENTION

The anionic cellulose ether according to the present invention isobtainable by a process comprising reacting an alkali metal cellulosewith

one or more reagents A selected from the group consisting of haloaceticacids, alkali metal haloacetates, alkali metal vinyl sulfonates, vinylsulfonic acid, and precursors thereof, and

one or more reagents B having the formula R¹—(OCH₂CH(R²))_(n)-P,

wherein

R2 represents hydrogen or a methyl group,

n is 0-2,

P represents a glycidyl ether group, a 1,2-epoxy group or a precursorthereof, if P represents a glycidyl ether group, R¹ represents a linearC₃-C₅ alkyl group, optionally containing an oxygen atom, a phenyl groupor a benzyl group, if P represents a 1,2-epoxy group, R¹ represents alinear C₃-C₅ alkyl, optionally containing an oxygen atom,

with the proviso that in the process no use is made of a reagent havingthe formula R³—(OCH₂CH(R⁴))_(m)-Q, wherein R³ represents a C₈-C₃₀ group,R⁴ represents hydrogen or a methyl group, m is 0-10, and Q represents aglycidyl ether group, a 3-halo-2-hydroxypropyl ether group, a 1,2-epoxygroup or a halide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows viscosity-temperature curves of BGE-CMC and CMC measuredwith spindle sc4-18 at a shear rate of 15.8 s⁻¹ in demineralized waterat pH 7;

FIG. 2 shows a viscosity-temperature curve of BGE-CMC measured withspindle sc4-34 at a shear rate of 0.17 s⁻¹ in demineralized water at pH7; and

FIG. 3 shows viscosity-temperature curves of BGE-HEC and HEC measuredwith spindle sc4-18 at a shear rate of 3.96 s⁻¹ in demineralized waterat pH 7.

DETAILED DESCRIPTION OF THE INVENTION

The inventive anionic cellulose ethers show a lesser decrease, or evenan increase, in viscosity with an increase in temperature.

Applicant's non-prepublished patent application PCT/EP98/03709 relatesto hydrophobically modified anionic cellulose ethers which areobtainable by a process comprising reacting an alkali metal cellulosewith at least three different alkylating reagents.

In the context of the present invention, by the terms precursor of analkali metal vinyl sulfonate, of vinyl sulfonic acid, of a glycidylether group, and of a 1,2-epoxy group are meant an alkali metal2-haloethane-1-sulfonate, a 2-haloethane-1-sulfonic acid, a3-halo-2-hydroxypropyl ether group, and a 2-halo-hydroxyethyl group,respectively.

The anionic cellulose ethers of the present invention typically have adegree of polymerization (i.e. DP) in the range of 40 to 4,000,preferably 100 to 3,000, a degree of substitution (i.e. DS) of thesubstituent that is derived from reagent A in the range of 0.3 to 1.6,preferably 0.5 to 1.4, more preferably 0.6 to 1.4, and a molarsubstitution (i.e. MS) of the substituent that is derived from reagent Bin the range of 0.05 to 1.5, preferably 0.1 to 0.8, more preferably 0.1to 0.5.

Suitable and readily available cellulose starting materials includecotton linters and purified high-alpha wood pulp.

Typically, the cellulose is reacted with an aqueous solution of analkali metal hydroxide to prepare an alkali metal cellulose, i.e.so-called alkalinization. Suitable alkali metal hydroxides includesodium hydroxide, potassium hydroxide, and lithium hydroxide, withsodium hydroxide being preferred.

Suitable reagents A for preparing the anionic cellulose ether of thepresent invention according to the process described above includechloroacetic acid, sodium chloroacetate, and sodium vinyl sulfonate. Amixture of, for example, chloroacetic acid and sodium vinyl sulfonatemay also be used, and this results in the preparation of ahydrophobically modified carboxymethyl sulfoethyl cellulose. It ispreferred that reagent A is, or consists essentially of, chloroaceticacid.

Preferably, R¹ represents a linear C₃-C₅ alkyl group, optionallycontaining an oxygen atom, more preferably a linear C₃-C₅ alkyl group,most preferably an n-butyl group. Preferably, R2 represents hydrogen.Preferably, n is 0 or 1, more preferably 0. Preferably, P is a glycidylether group.

Suitable reagents B include n-propyl glycidyl ether, n-butyl glycidylether, n-butoxyethyl glycidyl ether, phenyl glycidyl ether, benzylglycidyl ether, methoxyethyl glycidyl ether, ethoxyethyl glycidyl ether,and mixtures thereof. A particularly preferred alkylating reagent B isn-butyl glycidyl ether.

The process in accordance with the present invention may be conducted atany desired reaction temperature. Typically, it is carried out between20 and 125° C., preferably from about 55 to 105° C., for a sufficienttime to provide the desired levels of substitution, typically from about1 to 24 hours or more. The reaction may be conducted in a relativelylarge amount of diluent or with a minimal amount of diluent as desired,i.e., using either a so-called slurry or a so-called dry process.

In this specification, the term slurry process stands for a processwhere the weight ratio of liquid medium to cellulose is greater than 10,while a dry process means a process where the weight ratio of liquidmedium to cellulose is equal to or smaller than 10, preferably smallerthan 5, more preferably smaller than 3. Typically, a dry process iscarried out in a high-efficiency intensive mixer, e.g. a plowsharemixer.

Suitable diluents include ethanol, isopropyl alcohol, tert-butylalcohol, acetone, water, methylethyl ketone, and mixtures thereof.Preferred diluents are ethanol, isopropyl alcohol, water, and mixturesthereof. The use of water is particularly preferred.

It is preferred to carry out the process in accordance with theinvention by means of the so-called dry process using a minimal amountof diluent, in particular water, that is, just enough to allow thecellulose to swell while preventing dissolution.

The reaction is carried out using means and equipment well-known to aperson skilled in the art. The reaction vessel or reactor is suitablyequipped with a stirrer or mixing gear, a nitrogen inlet tube, acondenser, and facilities for heating. A particularly suitable reactoris a Drais® or a Lödige® reactor.

The amount of alkali metal hydroxide per sugar repeating unit may varydepending on the alkylating agents used, as is known to a person skilledin this art. Typically, an amount of between from 0.001 to 5 moles permole of sugar repeating unit is used. Depending on the nature of thealkylating reagent(s) used, additional alkali metal hydroxide is added.For instance, when using chlorinated alkylating agents, e.g.,chloroacetic acid, an additional molar equivalent of hydroxide isrequired.

Many polysaccharides when in contact with base are readily degraded byoxygen. Accordingly, it is preferred to exclude oxygen from the reactionvessel during the time the alkali metal hydroxide is present. Thereaction is suitably carried out in an atmosphere of an inert gas,preferably nitrogen.

After the reaction of the cellulose with a suitable amount of an aqueoussolution of an alkali metal hydroxide, the alkali metal cellulose may bereacted (i.e. alkylated) first with alkylating reagent A, followed by areaction with alkylating reagent B, at a suitable temperature and for atime sufficient to provide the desired levels of substitution.Alternatively, alkylating reagent B may be added first, after whichalkylating reagent A is allowed to react, or the alkali metal cellulosemay be simultaneously reacted with alkylating reagents A and B. Afurther alternative reaction path is to first add a small amount ofreagent A, then reagent B, and finally the remainder of reagent A.

The process in accordance with the present invention may also be carriedout by starting from a suitable commercially available cellulosederivative intermediate such as carboxymethyl cellulose (CMC) or itssodium salt. In that case, preferably a technical grade CMC is used. Itwas found that when a higher grade, purified CMC, which does not containsodium chloride, was used, the yield was reduced. When using a purifiedCMC, yields could be restored by the addition of sodium chloride to thereaction mixture.

Preferably, the cellulose, in the form of fibres, linters or a powder,is allowed to react with an aqueous solution of an alkali metalhydroxide and the obtained alkali metal cellulose is reactedsimultaneously with reagents A and B, with the temperature graduallybeing increased from about room temperature to about 105° C. Thereagents A and B can be added in the pure form or as a solution in adiluent, e.g., a solution of chloroacetic acid in ethanol.

A more preferred embodiment of the process in accordance with thepresent invention is a preferably dry process in which reagent A isreacted with the alkali metal cellulose in the presence of an alcohol,in particular isopropanol or ethanol, followed by reaction with reagentB in the presence of water. Typically, the amount of water presentduring alkylation is 2 to 12 moles per mole of sugar repeating unit.Preferably, an amount of 3.5 to 10 moles/mole is used.

A person skilled in the art will have no trouble selecting suitableamounts of reactants per sugar repeating unit for the process definedabove. For reagent A an amount of 0.3 to 3.5 moles per mole of sugarrepeating unit is suitable, an amount of 0.5 to 2.5 moles/mole beingpreferred. For reagent B an amount of 0.02 to 2.5 moles/mole issuitable, an amount of 0.05 to 1.5 moles/mole being preferred. Withthese amounts, yields in the range of 20 to 60% can be obtained. Ifdesired, however, higher amounts may also be used.

In another embodiment of the process in accordance with the presentinvention, a third alkylating reagent, i.e. a quaternary ammoniumalkylating reagent C or a nonionic alkylating reagent D, is used.Typically, this substituent is introduced after the reaction of alkalimetal cellulose with reagents A and B, but it may also be introducedearlier. Typically, reagent C is a 3-trialkylammonium-1,2-epoxypropanehalide wherein each alkyl group independently is a C₁-C₂₄ alkyl group.Suitable alkyl groups include methyl, ethyl, propyl, benzyl, and C₈-C₂₄fatty alkyl groups. Preferably, 3-trimethylammonium-1,2-epoxypropanechloride or 1-chloro-2-hydroxy-3-trimethylammonium-propane chloride isused. Suitable reagents D include ethylene oxide, propylene oxide,methyl chloride, ethyl chloride, 3-chloro-1,2-propanediol, glycidol, andmixtures thereof.

Without wishing to be bound by any particular theory, Applicant believesthat the reaction of alkali metal cellulose with the glycidyl ethers andepoxides—in particular glycidyl ethers—in accordance with the presentinvention results in the formation of cascadic structures of theglycidyl ether and/or epoxide groups due to the fact that, for example,the secondary hydroxy group which is formed after the reaction of alkalimetal cellulose with n-butyl glycidyl ether is more reactive than any ofthe hydroxy groups of the cellulose itself, and so on. Hence, this leadsto structures in which —[OCH₂CH(CH₂O-n-Bu)]_(n)OH groups are attached toone or more cellulose glucose units, wherein n typically is in the rangeof 2-3. Said groups may also be carboxymethylated. It will be clear thatthe final structure of the anionic cellulose ether of the presentinvention is dependent on the order of addition of reagents A and B andon the reaction conditions used when performing the alkylationreactions, such as the amount of alkali metal hydroxide and the type andamount of diluent.

With the changes in structure of the anionic cellulose ether, theviscosity-temperature profile may also be influenced.

The invention is illustrated by the following examples.

EXAMPLES

Materials:

Linters Cellulose (0.5 mm milled), ex Buckeye

n-Butyl glycidyl ether, 95%, ex CFZ Chloroacetic acid, 99%, ex AkzoNobel

The reactions were carried out in a Drais® Turbulent Mixer, type TR2.5,reactor. The knife blades were rotated at 180 rpm. The reactor washeated by a Thermomix UB water/oil bath.

The DS values were determined using a 300 MHz Bruker NMR spectrometer,as specified by F. Cheng et al. in Journal of Applied Polymer Science,Vol. 61, 1831-1838 (1996). MS values were determined accordingly. CMstands for carboxymethyl, BGE for n-butyl glycidyl ether, and HE forhydroxyethyl. The viscosity was recorded using a Brookfield DVIIIrheometer equipped with a small sample adaptor using an appropriatespindle.

Example 1

An aqueous solution of 40 wt % sodium hydroxide (202 g) was added to astirred mixture of cellulose (150 g) and 40 ml of water under a nitrogenatmosphere at 20° C. After 90 minutes an aqueous solution of 80 wt %chloroacetic acid (95.6 g) and n-butyl glycidyl ether (120 g) was added.Then the mixture was heated slowly to 95° C. and stirred for 8 hours.The reaction mixture was cooled, neutralized with acetic acid, washedwith ethanol and acetone, and was dried under reduced pressure at 70° C.A white powder, i.e. n-butyl glycidyl carboxymethyl cellulose (BGE-CMC),was obtained in a yield of 47% with the following analysis (NMR):DS_(CM) 0.74, MS_(BGE) 0.47.

When BGE-CMC was dissolved in water, an almost clear, shear-thinningsolution was obtained.

Example 2

An aqueous solution of 40 wt % sodium hydroxide (202 g) was added to astirred mixture of cellulose (150 g), 40 ml of water, and n-butylglycidyl ether (120 g) under a nitrogen atmosphere at 20° C. After 1hour the mixture was heated at 80° C. for 23 hours. The mixture wascooled, and 450 ml of ethanol were added. Then a solution ofchloroacetic acid (77.5 g) in 23 ml of ethanol was added, and themixture was heated at 60° C. for 90 minutes and at 75° C. for 30minutes. The mixture was cooled and neutralized with acetic acid. Thecrude reaction product was washed with ethanol and acetone, and wasdried under reduced pressure at 70° C. A white powder (BGE-CMC) wasobtained with the following analysis (NMR): DS_(CM) 0.70, MS_(BGE) 0.32.

Example 3

An aqueous solution of 40 wt % sodium hydroxide (50 g) was added to astirred mixture of carboxymethyl cellulose (215 g) with a DS_(CM) of0.85, n-butyl glycidyl ether (120 g), and an aqueous solution of 20 wt %sodium chloride (170 g). Then the reaction mixture was heated slowly to95° C. and stirred for 6 hours, after which it was cooled, neutralizedwith acetic acid, washed with ethanol and acetone, and dried underreduced pressure at 70° C. An off-white product (BGE-CMC) was obtainedwith the following analysis (NMR): DS_(CM) 0.85, MS_(BGE) 0.47.

The viscosity-temperature profile of this compound is shown in FIG. 1(see below).

Example 4

The change in viscosity of an aqueous solution of an anionic celluloseether in accordance with the present invention with increasingtemperature was recorded. The results are shown in FIGS. 1 and 2.

FIG. 1 shows the viscosity-temperature curves of BGE-CMC (the product ofExample 3) and CMC at a relatively high shear rate.

FIG. 2 shows the viscosity-temperature curve of a different sample ofBGE-CMC at a relatively low shear rate.

From these Figures it can be concluded that an anionic cellulose etheraccording to the present invention (BGE-CMC) shows an increase inviscosity with increasing temperature, whereas an anionic celluloseether of the prior art (CMC) shows a marked decrease.

This viscosity-temperature effect was not observed for a sample ofBGE-CMC containing n-butoxyethanol, which is known to prevent or destroyassociation.

Comparative Example A

An aqueous solution of 40 wt % sodium hydroxide (100 g) was added to astirred mixture of hydroxyethyl cellulose (350 g), 40 ml of water,t-butanol (50 g), and n-butyl glycidyl ether (90 g) under a nitrogenatmosphere. After 45 minutes the mixture was heated to 95° C. and wasstirred at this temperature for 4 hours. The mixture was cooled andneutralized with acetic acid. For analysis, a small sample was taken upin water, precipitated in acetone, filtered, washed with acetone, anddried. A brown powder, i.e. n-butyl glycidyl hydroxyethyl cellulose(BGE-HEC), was obtained with the following analysis (NMR): MS_(SH) 1.7,MS_(BGE) 0.28.

Comparative Example B

The viscosities of aqueous solutions of HEC and BGE-HEC with increasingtemperature were recorded. The results are shown in FIG. 3. A 3 wt %aqueous solution of these cellulose ethers had to be prepared in orderto obtain a measurable viscosity.

From this Figure it can be concluded that these nonionic celluloseethers of the prior art show a marked decrease in viscosity withincreasing temperature and that this effect is more pronounced in thecase of BGE-HEC.

What is claimed is:
 1. An anionic cellulose ether obtainable by aprocess comprising reacting an alkali metal cellulose with one or morereagents A selected from the group consisting of haloacetic acids,alkali metal haloacetates, alkali metal vinyl sulfonates, vinyl sulfonicacid, and precursors thereof, and one or more reagents B having theformula R¹—(OCH₂CH(R²))_(n)-P,  wherein R² represents hydrogen or amethyl group, n is 0-2, P represents a glycidyl ether group, a 1,2-epoxygroup or a precursor thereof, if P represents a glycidyl ether group, R¹represents a linear C₃-C₅ alkyl group, optionally containing an oxygenatom, a phenyl group or a benzyl group, if P represents a 1,2-epoxygroup, R¹ represents a linear C₃-C₅ alkyl group, optionally containingan oxygen atom, with the proviso that in the process no use is made of areagent having the formula R³—(OCH₂CH(R⁴))_(m)-Q, wherein R³ representsa C₈-C₃₀ group, R⁴ represents hydrogen or a methyl group, m is 0-10, andQ represents a glycidyl ether group, a 3-halo-2-hydroxypropyl ethergroup, a 1,2-epoxy group or a halide.
 2. The ether according to claim 1,wherein reagent A is chloroacetic acid.
 3. The ether according to claim1, wherein R¹ represents a linear C₃-C₅ alkyl group, optionallycontaining an oxygen atom.
 4. The ether according to claim 1, wherein R2represents hydrogen.
 5. The ether according to claim 1, wherein n is 0.6. The ether according to claim 1, wherein P represents a glycidyl ethergroup.
 7. The ether according to claim 1, wherein reagent B is n-butylglycidyl ether.
 8. The ether according to claim 1, wherein the processis a dry process.
 9. The ether according to claim 1, wherein the alkalimetal cellulose is reacted with reagent A in the presence of an alcohol,followed by reaction with reagent B in the presence of water.
 10. Anassociative thickener comprising the ether of claim
 1. 11. A rheologymodifier comprising the ether of claim
 1. 12. A stabilizer comprisingthe ether of claim
 1. 13. A method of reducing fluid loss while drillingwhich comprises utilizing the ether of claim 1.